Cleaning of metallic surfaces



T A. EDISON.

CLEANING 0F METALLIC SURFACES.

APPLICATION FILED JULY 3. 1919.

1,869,271, Patented Feb. 22, 1921 UNITED STATES PATENT orr cs.

THOMAS A. EDISON, 0F LLEWEIIILYN PARK, WEST ORANGE, NEW J ER SEY.

CLEANING or METALLIC soaraons.

Specification of Letters Patent. 7 Patented Feb, 22, 1921.

Application filed July 3, 1919. Serial No. 308,379.,

To all whom it may comic-1w. Be it known that I, Tuonns A. EDISON, acitizen of the United States, and a resident of Llewellyn Park, \VestOrange, Essex county, New Jersey, have invented certain new and usefulImprovements in Cleaningof Metallic Surfaces, of which the following isa description.

Hy-invention relates to the cleaning of metallic surfaces and moreparticularly to the cleaning of the surfaces of metallic objectselectrolytically preliminary to subsequent treatment by which thesurfaces so cleaned are coated with another metal or material, as, forexample, in processes of electro-plating, amalgamating. tiuniug.galvanizing, enameling, etc., or in the process of coating such asurface with a thin layer or film of a selenide as described in mycopending application Serial No. 305,821, filed June 21, 1919, andentitled Electro-plating.

Heretofore, in cleaning the surfaces of metallic objectselectrolytically, it has been customary to employ an electrolytic cellcomprising electrolyte such as a solution of caustic soda, causticpotash or the like, an anode composed of a suitable material which willnot dissolve in the electrolyte, and the metal to be cleaned opposed .tosaid anode in the electrolyte as a cathode. With the use of such anelectrolytic cleaning solution, however, it often happens that thedirtis not completely removed from the cathode, that is, the metal to becleaned,- and moreover, a black deposit is usually formed on thecathode, probably due to the presence of more or less foreign materialin the caustic soda orcaustic potash, as it is impossible to obtain thelatter in a pure state.

The principal object of my invention is to provide an improvedelectrolytic cell including an improved electrolyte therefor, wherebymetallic surfaces may be quickly and completely cleanedelectrolytically, and whereby no deposit of foreign material will beformed on the surfaces so cleaned.

My invention also resides in an improved process for cleaningmetallicsurfaces electrolytically. v I

I have discovered that the foregomg results may-be obtained upon thepassage of a current of sufiicient density through an electrolytic cellcomprising an electrolyte consisting of a slightly alkaline and nearlysaturated solution of a metal of the alkali.

of the metal to be cleaned andopposed to the' anode 3 in the electrolyte2. The anode 8 and the cathode 4 are respectively suitably supported, asby means of heavy clamps 5 formed of conducting material, from a pair.

of bars 6 and 7 of conducting material carried by the tank 1. A pair ofconductors 8 and 9, respectively connected with the anode and cathode,serve to supply the cell with current from any suitable source (notshown).

. The electrolyte 2 preferably consists of a nearly saturated solutionof either sodium sulfate or potassium sulphate rendered slightlyalkaline by the addition of a s'uf- -ficient amount of a hydroxid of ametal of thealkali group, preferably caustic potash or caustic soda; andwhen such an electrolyte is employed, the anode is preferably formed ofpure carbon, such as graphite, which is only slightly attacked byelectrolysis in the electrolytic solution. 'I find that graphite -ispreferable over other forms of carbon, owing to its insolubility in analkaline solution when subjected to electrolysis.

In order to effect the cleaning of the surface of the cathode 4consisting of the metal to be cleaned, a current equivalent to about 150amperes per square foot of such surface is passed through the cell. Thepassage of this current results in the evolution of the alkali metal andsimultaneously, due to the decomposition of the water in theelectrolyte, in the evolution or generation of'great quantities ofhydrogen gas on the surface of the cathode. This hydrogen gas indetaching itself from the cathode mechanically strips off or detachesthe foreign matter so as to leave an absolutely clean surface. Thisresult is facilitated by reason of the fact that oil, grease, dirt andother forelgn material are more or less porous so that the gas has anopportunity of forcibly detach- I: stantially as described."

ing itself from the surface to carry the foreign material with it. Thisaction is almost entirely mechanical, though the oil and.

grease are eventually decomposed to a great extent by the alkali. Thenascent potassium or sodium evolved. in the cell, primarily on thecathode, also reduces any oxid of the metal of which the cathode isformed and which may. be present on such cathode, to metal. i

lVhen a current of the density above mentioned is passed through thecell, all grease and other dirt and impurities are completely removedfrom the surface of the metal to be cleaned, that is, from the cathode4, in from washed, after which it is ready for subsequent treatment, forexample, the application thereto of a coating such as a film consistingof a selenide, which may be formed thereon in the manner described in myapplication above referred to.

Having now described my invention, what I claim as new and desire toprotect by Letters Patent of the United States is as follows celladapted to be employed for cleaning metals, comprising an alkalinesolution of a sulfate of a metal of the alkali group, substantially asdescribed.

2. An electrolyte for use in an electrolytic cell adapted to be employedfor cleaning metals, comprising a solution of a sulfate of a metal ofthe alkali group and a. hy-

lVhere a cell droxid of a metal of the alkali group, sub- 3. Anelectrolyte for use in an electrolytic cell-adapted to be employed forcleaning metals, comprising a solution of a sulfate of a metal of thealkali group and a hydroxid of potassium or sodium, substantially asdescribed.

4. An electrolyte for use in an electrolytic cell adapted to be employedfor cleaning metals, comprising a nearly saturated solu-- tion of asulfate'of a metal of the alkali group-containing an amount of ahydroxid of a metal of the alkali group suflicient ,to render the sameslightly alkaline, substantially as described.

5. An electrolytic cell for cleaning metals, comprising an electrolyteconsisting of a solution of a sulfate of a metal of the alkali group, ananode formed of graphite, and a cathode consisting of the metal to becleaned, substantially as described.

-6. The method of cleaning a metal electrolytically, which consists inemploying the metal to be cleaned as a cathode opposed to a suitableanode in an electrolyte consisting of an alkaline solution of a sulfateof a metal of the alkali group, and passing through the electrolyticcell a current equivalent to approximately 150 amperes per squarefootvof the surface to be cleaned, substantially as described.

7. The method of cleaning a metal electrolytically, which consists inemploying the suitable anode in an electrolyte consisting of an alkalinesolution of a sulfate of a metal 1. An electrolyte for use in anelectrolytic of the alkali group, and passing through the electrolyticcell for a period of from approximately'l to 5 minutes acurrent'equivalent to approximately 150 amperes per square foot ofthesurface to be cleaned, substantially as described.

'on signed this 24th day of

